Operating voltage supply arrangement for cathode-ray tube apparatus



Jan. 2, 1951 Filed May 16, '1947 s. FORBES ET AL ,536,497 OPERATINGVOLTAGE SUPPLY ARRANGEMENT FOR CATHODE-RAY TUBE APPARATUS 2 Sheets-Sheet1 1 Tvm SUPPLY 1 Q 2a, JY/vc. M0701? GONIOML-IM SIGN/71. GEN.

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[an Saar! f'orbes S- AZmneib Wl/iam Gaol-ye flqz'rod ATTORNEY PatentedJan. 2, 1951 OPERATING VOLTAGE SUPPLY AR- RANGEMENT FOR TUBE APPARATUSCATHODE-RAY Ian Stuart Forbes, Chelmsiord, and Knneth William GeorgeHarrod, Little Baddow, England,

assignors,

by mesne assignments, to Radio Core poratlon of America, New York, N.Y., a corporation of Delaware Application May 16, 1947, Serial No.748.430

' In Great Britain May 20, 1946 Claims. (Cl. 343*118) This inventionrelates to operating voltage supply arrangements for cathode ray tubeapparatus and more particularly to such apparatus of the kind in which acathode ray tube is employed in functional corelationship with amotordriven moving member, so'as to display, indicate or measure signalswhich are expected to vary as said member is moved. An example of thiskind of apparatus is provided .by radio direction finders of thespinning radio goniometer or spinnin aerial type, wherein a motor drivendirectional aerial is continuously rotated and the signals derivedtherefrom displayed by means of a cathode ray tube subjected todeflection control by a time base circuit synchronised with the aerialrotation. Another example of apparatus of the kind referred to isprovided by oscilloscope apparatus employed for taking heat engineindicator diagrams, against a base line which-should correspond topiston displacement. In such a case if the engine run at varying speedthe diagram will not be of constant length a as is desired for ease ofsubsequent calculations. There are numerous other examples of cathoderay tube apparatus wherein the time deflection of the tube is requiredto be accurately co-related with the movement of a driving memher whichin the case of the direction finder mentioned is the rotating aerial andin the case of an engine indicator diagram apparatus is a moving part ofthe engine.

The importance of maintaining constant operating voltages to cathode raytubes employed in apparatus of the kind referred to is in general wellrecognised and it is common practice to provide stabilised voltagesupplies to the various electrodes of the tube, as well as to amplifierdeflection circuits and the like associated therewith. It has now beenfound, however, that despite the provision of careful stabilisation ofvoltage supply comparatively serious errors can occur by reason ofvariation in speed of the driving member due to variation in frequencyof an alternating current supply employed to energise a motor drivingsaid member. The magnitude and importance of the errors which may occurmay be exemplified by taking the case of a radio direction finder of thespinnin radio goniometer type, wherein the aerial is rotated by an A. C.motor supplied from A. C. mains. If the frequency of the supply changesby 5%, the result of the consequent changes in the speed of the motormay produce a bearing error of the order of 9 degrees. The presentinvention 'seeks to obviate this type of diiiiculty and reduce thecorresponding errors to small proportions.

According to this invention a cathode ray tube apparatus of the kindreferred to is characterised in that the time base or deflection controlof the tube is subjected to corrections in dependence upon departuresfrom a predetermined value of the speed of a motor driving theassociated moving member, so as to correct for or substantially reducevariations in indication or measurement which would otherwise resultfrom said departures.

The invention is illustrated in the accompanying drawings which show twoembodiments in block diagram form. The same references are used for likeparts in both figures in which electrical energy supply paths arerepresented by single lines with arrow heads thereon and mechanicaldrives are represented by shafts with arrow heads adjacent them.

Referring to Fig. 1 which shows in block diagram form one embodiment ofthis invention as applied to a radio direction finder of the spinningradio goniometer type a mains or other A. C. supply connected at I isutilised to drive a motor 2, for example an induction or a synchronousmotor, the shaft 2a of which mechanically drives the spinningdirectional aerial or radio goniometer unit 3 and also mechanicallydrives a source 4 of pulsed or other synchronising signals for thecathode ray tube. The unit 3 includes any well known suitableequipmentpreferably a radio-goniometer-giving an electrical output whichvaries with the position of the rotating parts, which variation it isrequired to observe. Since the motor 2 is of the synchronous orinduction type its speed will be dependent on the Supply frequency, butsubstantially independent of the supply voltage. Electrical output fromthe synchroniser 4 is taken to a shaping circuit or converter 5 or otherdevice which converts the said output into a wave shape suitable forapplication to a time base circuit 6. The converter 5 receives itselectrical power supplies from a stabilised voltage source 1 fed fromthe main supply. This stabilised voltage source 1 also supplieselectrical power to the time base circuit 6. The mains or other A. C.supply from I is also passed through a frequency discriminator circuit 8which in turn feeds through a suitable voltage supply unit 9 to the timebase circuit 6. The voltage supply to the time base circuit 6 throughthe channel 8-9 determines the velocity of the time base sweep and sincethe said channel includes the discriminator circuit 8 the voltagesupplied therethrough' will vary according to the frequency. The supplyunit 9 is such that its output varies according to its own inputvoltage,

but is substantially independent of its own input frequency and sincethis input voltage is caused by the discriminator circuit 8 to be afunction of the frequency receive the required correctin voltage. Thesaid time base circuit 6 supplies one input to the deflection amplifiercircuits at H) which receive a second input from the spinning aerial, orradio goniometer unit 3. The output from unit I is fed to the deflectionmeans (electrostatic plates or the like) of the cathode ray tube II. Thedeflection amplifier l0 receives stabilised power from-a unit l2energised from the mains or other supply and the various cathode raytube electrodes also receive stabilised power as required through asimilar unit l3.

It has been found that with an arrangement as just described a variationin frequency of as much as 10%, even when combined with voltage changesof the same order in any combination,

do not produce bearing errors in excess of one degree.

In the modification shown in Fig. 2 the frequency discriminator 8 (whichmay be, as in Fig. 1 a fiux regulated stabilising transformer whoseoutput is substantially independent of input voltage but dependent onlyon input frequency and which is arranged in known manner to provide anoulput which varies linearly with input frequency over a wide only tounit I but also to the units 9 and I3. The former unit 9 may be arectifier providing D. C. supply at, for example, about 1000 volts, tothe time base charging circuit 6 the actual voltage, of course,depending on the input frequency to unit 8. The said unit 9 alsosupplies'voltage to the deflecting amplifier circuits at I0 and to thetube at H. In this case the deflecting amplifiers are so designed thattheir sensitivity is substantially independent of supply voltage. Theoutput from unit 1 which may, for example, be a rectifier giving astabilised voltage of approximately 200 volts D. C. feeds units and 6 asin Fig. 1 am also supplies voltage to unit 10. In Fig. 2 an an. plifierI4 is shown interposed in the feed from unit 3 to unit "I.

The actual voltage values required will varyfrom case to case and dependupon design details. In general, however, about 2000 volts negative willbe required for the cathode ray tube at H; about 1000 volts positive forthe deflection amplifier circuits at ID, the final anode of the cathoderay tube at H and for the usual resistancecapacity circuits in the timebase at 6; and additional supplies at about 250 volts and 500 voltspositive for other operating potentials in the deflection and otheramplifiers.

Although an important application of the invention is to radio directionfinders this is not the only application and the said invention may beemployed in any cathode ray app ratus of the kind referred to.

Having now particularly described and ascertained the nature of our saidinvention and in from I the time base 6 will range) provides input notwhat manner the same is to be performed we deby said shaft to providefurther signals whose phase relationship to said timing signals is to beindicated, a cathode ray oscilloscope, means for deflecting the cathoderay beam of said oscilloscope along one axis in response to said furthersignals, a time base signal generator responsive to said timing signalsto deflect said beam along another axis, and means responsive to thespeed of said shaft to control the amplitude of the output of said timebase signal generator.

2. The invention as set forth in claim 1, wherein said motor is analternating current motor driven from an alternating current supp andthe amplitude of said time base signal varies according to the departureof the frequency of said supply from a predetermined frequency.

3. A radio direction finder system including a goniometer, a motorcoupled to said goniometer, and rotating at a speed which is nominallyconstant but is actually subject to variations, a cathode rayoscilloscope, means for deflecting the cathode ray beam of saidoscilloscope in response to the output of said goniometer, asynchronizing system generator coupled to said motor and driven therebyto provide timing signals, a time base signal generator responsive tosaid timing signals to deflect said cathode ray beam along a secondaxis, and means responsive to the speed of said motor to control theamplitude of the output of said time base signal generator.

4. An indicator system including a shaft, an alternating current supply,and an alternating current motor rotating said shaft at a speed which isnominally constant but is, subject to variations owing to variations inthe frequency of said supply, a device driven by said shaft to providesignals whose phase is to be indicated, a cathode ray oscilloscope,means for deflecting the cathode ray beam of said oscilloscope along oneaxis in response to said signals, a synchronizing signal generatorproviding timing signals whose frequency varies with variation in thefrequency of said alternating current supp a time base signal generatorresponsive to said timing signals to deflect said cathode ray beam alonganother axis, and means responsive to the frequency of said alternatingcurrent supply to control the amplitude of the output of said time basesignal generator.

5. The invention as set forth in claim 4, wherein said last-mentionedmeans includes a discriminator producing an, output voltage whichdepends upon the input frequency over a predetermined range and issubstantially independent of input voltage over said range, and meanssupplying said output voltage to said time base signal generator.

IAN STUART FORBES. KENNETH WILLIAM GEORGE HARROD.

file of this patent:

UNITED STATES PATENTS Number Name Date 2,180,365 Norton Nov. 21, 19392,170,847 Banks Aug; 29, 1939 2,222,943 George Nov. 26, 1940 2,233,374Johnske et al Feb. 25, 1941 2,369,631 Zanarini Feb. 13, 1945 2,408,041Busignies Sept. 24, 1946 FOREIGN PATENTS Number Country Date 577,795Great Britain May 31,1946 601,655 Great Britain Mayll, 1948

